Field of the Invention
The present invention relates to wireless communications, and more particularly, to a relay UE selecting method performed by a UE in a wireless communication system, and a UE using the same.
Related Art
In International Telecommunication Union Radio communication sector (ITU-R), a standardization task for International Mobile Telecommunication (IMT)-Advanced, that is, the next-generation mobile communication system since the third generation, is in progress. IMT-Advanced sets its goal to support Internet Protocol (IP)-based multimedia services at a data transfer rate of 1 Gbps in the stop and slow-speed moving state and of 100 Mbps in the fast-speed moving state.
For example, 3rd Generation Partnership Project (3GPP) is a system standard to satisfy the requirements of IMT-Advanced and is preparing for LTE-Advanced improved from Long Term Evolution (LTE) based on Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier-Frequency Division Multiple Access (SC-FDMA) transmission schemes. LTE-Advanced is one of strong candidates for IMT-Advanced.
There is a growing interest in a Device-to-Device (D22) technology in which devices perform direct communication. In particular, D2D has been in the spotlight as a communication technology for a public safety network. A commercial communication network is rapidly changing to LTE, but the current public safety network is basically based on the 2G technology in terms of a collision problem with existing communication standards and a cost. Such a technology gap and a need for improved services are leading to efforts to improve the public safety network.
The public safety network has higher service requirements (reliability and security) than the commercial communication network. In particular, if coverage of cellular communication is not affected or available, the public safety network also requires direct communication between devices, that is, D2D operation.
A D2D operation is also referred to as a proximity service (ProSe) operation in view of signal transmission and reception between neighboring devices and has various advantages. For example, a D2D user equipment (UE) may perform data communication with a high transmission rate and low delay. Further, the D2D operation may distribute traffic concentrated on a base station, and may also function to extend the coverage of the base station if the D2D UE serves as a relay.
The D2D UE may also operate as a UE serving as a relay to connect a sidelink and a cellular link. That is, the D2D UE may operate as a relay UE.
A relay UE may serve as a relay between a specific UE and a network, in which the specific UE may be referred to as a remote UE. A remote UE may select a relay UE, in which it is necessary to specify a method for selecting a relay UE.
Particularly, if a remote UE uses only a process of comparing a measurement of a link between the remote UE and a candidate relay UE with a determined threshold to select a relay UE, a network hardly intervenes in the relay UE selecting process. That is, it is difficult for the network to control the process for the remote UE to select the relay UE.